1. Field of the Invention
The invention relates to thermoplastic multilayer composites of polyamide and polyvinylidene fluoride.
2. Discussion of the Background
There is a series of applications for which polyamides and polyvinylidene fluoride are unsuitable. Polyamides are, for example, not resistant to weathering, since they age on exposure to light and also absorb atmospheric moisture. This leads to discoloration, deterioration of the mechanical properties and distortion. Although polyamides have good mechanical properties, in particular good toughness, they have poor barrier action; thus polar materials can easily migrate through polyamides. This is a great disadvantage, for example, in the case of fuel pipes through which alcohol-containing fuel is conveyed.
Polyvinylidene fluoride generally has good weathering resistance and good chemical resistance. Furthermore, polyvinylidene fluoride has an excellent barrier action with respect to both polar and nonpolar media. However, polyvinylidene fluoride is impact sensitive. In particular, the notched impact strength is insufficient for general use.
It is conventionally known that the majority of polymers, including polyamide and polyvinylidene fluoride (PVDF), are incompatible with one another. However, an adhesive thermoplastic multilayer composite is extremely desirable for industrial applications.
Thermoplastic multilayer composites of PVDF and polyamide moulding compounds are known per se in numerous embodiments. However these are all not adequate for use in industrial applications. Moulding compounds and the thermoplastic multilayer composites produced therefrom should meet the following requirements:
1. The moulding compounds of PVDF and polyamide should adhere strongly to one another in the thermoplastic multilayer composite. PA1 2. The thermoplastic multilayer composite of PVDF and the polyamide moulding compounds should be resistant to fuels. PA1 3. The typical properties of the moulding compounds should not be altered by the modifications which are necessary to meet requirements 1 and 2. PA1 (I). at least one layer comprising moulding compound of polyamide, and PA1 (II). at least one layer adjacent to layer (I) comprising a moulding compound comprising a mixture of: PA1 i) from 14 to 85% by weight, preferably from 30 to 70% by weight, based on the total weight of component (IIb) of ##STR1## ii) from 10 to 75% by weight, preferably from 20 to 40% by weight, based on the total weight of component (IIb) of ##STR2## iii) from 0 to 15% by weight, based on the total weight of component (IIb) of ##STR3## iv) from 7 to 20% by weight, preferably from 8 to 12% by weight, based on the total weight of component (IIb) of ##STR4## where Alkyl is methyl, ethyl, propyl, butyl, or hexyl; and R.sub.1 to R.sub.4, identical or different, are hydrogen or (C.sub.n H.sub.2n+1) where n is an integer of from 1 to 6. Preferably R.sub.1 to R.sub.4 are methyl. Likewise, Alkyl is preferably methyl.
French Patent 2,602,515 describes a two-layer pipe having an outer layer of nylon 11 and an inner layer of plasticized polyvinylidene fluoride. However, an adhesive bond between the layers is not present; thus, pipes made from these layers do not meet the first requirement.